1. Field of the Invention
The present invention relates to a ceramic honeycomb structural body used for an automobile monolith catalyst converter.
2. Description of the Prior Art
An automobile monolith catalyst converter is generally constructed of a ceramic honeycomb structural body having numerous parallel channels depositing a catalytic meal, a casing, and supporting members holding the honeycomb structural body and the casing.
The catalyst converter is concurrently subjected to thermal action owing to an exhausted gas at high temperatures and to mechanical shock of engine vibration and driving road vibration and the like.
Ceramic honeycomb structural bodies are brittle against vibration and shock and are readily broken and further have a much lower thermal expansion coefficient than the above described catalyst casing and supporting members.
Accordingly, serious consideration has been heretofore given to the structure wherein the ceramic honeycomb structural body is held in the catalyst casing through supporting members.
Thus, it is necessary that the ceramic honeycomb structural body is clamped with a given compressed force through elastic supporting members so as not to break the ceramic honeycomb structural body owing to impact or rubbing of the ceramic honeycomb structural body against the catalyst casing, due to the above described vibrations, and that the honeycomb structural body is clamped with such a sufficient compressed force even at high temperatures that the abutting surfaces of the ceramic honeycomb structural body and the supporting members do not separate due to the difference of the thermal expansion coefficients. A variety of devices have been made with respect to the structure, material quality and shape of the supporting member.
In the automobile monolith catalyst converters having the structure wherein circumferential portions on both end surfaces of a ceramic honeycomb structural body are clamped by annular supporting members, each having a surface perpendicular to axis of the channels of the honeycomb structural body, having substantially uniform thickness and density with said perpendicular surface to the axis of the channels, there have been the following proposals. As shown in FIG. 1, heat resistant annular supporting member 1 having elasticity, which is composed of metal fibers, such as stainless steel, ceramic fibers or a combination thereof, has been proposed. Alternatively, as shown in FIG. 2, an annular supporting member 1 provided with an arm portion 3 having a sufficient longitudinal length which is elongated by the thermal expansion to compensate the separation due to the difference of the above described thermal expansion coefficients, is provided in the catalyst casing 2.
These proposals have the good elasticity to solve the problem caused from the above described difference of thermal expansion, and the ceramic honeycomb structural body is always clamped with moderate compressed force, but the edge of end surface of the ceramic honeycomb structural body is broken and unpurified exhausted gas leaks from the broken portions while the purifying ability is deteriorated. The break is further increased, and finally, the ceramic honeycomb structural body is put out of the supporting members and the purification becomes infeasible.
The breakage problem of the ceramic honeycomb structural body noted above is solved by reducing the compressed force applied to the end surfaces of the ceramic honeycomb structural body from the supporting members, but if the above described compressed force is reduced, as mentioned above, the breakage occurs due to the vibration, or, the unpurified exhausted gas is discharged through space between the inner surface of the catalyst casing and the outer circumferential side surface of the ceramic honeycomb structural body, thereby deteriorating the purifying ability. Therefore, the ceramic honeycomb structural body which does not cause breakage even if the honeycomb structural body is clamped with higher compressed force is needed.